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https://issues.apache.org/jira/browse/LUCENE-4764?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13575192#comment-13575192
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Robert Muir commented on LUCENE-4764:
-------------------------------------
{quote}
The problem is that packed-ints is only good if you know something about the
numbers, i.e. their size, distribution etc. But with category ordinals, on this
Wikipedia index, there's nothing "special" about them. Really every document
keeps close to arbitrary integers between 1 - 2.2M
{quote}
{quote}
If the following math holds – 25 ords per document
{quote}
Right but i dont look at what its doing this way. Today the ords for the
document are vint-deltas (or similar) within a byte[] right?
So instead perhaps the codec could encode the "first ord" (minimum) for the doc
in a simple int[] or whatever, but the additional deltas are all within a big
packed stream or something like that.
In all cases i like the idea of a specialized docvaluesformat for facets. it
doesn't have to be one-sized-fits-all: it could have a number of strategies
depending on whether someone had 5 ords/doc or 500 ords/doc for example, by
examining the iterator once at index-time to decide.
> Faster but more RAM/Disk consuming DocValuesFormat for facets
> -------------------------------------------------------------
>
> Key: LUCENE-4764
> URL: https://issues.apache.org/jira/browse/LUCENE-4764
> Project: Lucene - Core
> Issue Type: Improvement
> Reporter: Michael McCandless
> Assignee: Michael McCandless
> Fix For: 4.2, 5.0
>
> Attachments: LUCENE-4764.patch
>
>
> The new default DV format for binary fields has much more
> RAM-efficient encoding of the address for each document ... but it's
> also a bit slower at decode time, which affects facets because we
> decode for every collected docID.
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